Collagen is a polypeptide substance comprising one third of the total protein in mammalian organisms. It is the main constituent of skin, connective tissue, and the organic substance of bones and teeth. Collagen production in the body is preceded by the formation of a much larger molecule, the biosynthetic precursor procollagen, which is degraded by specific enzymes to form collagen.
Different types of collagen exist. They are all composed of molecules whose predominant feature is a triple helical rod or fibrillar conformation to fill in extracellular space. The amino acid sequence of the a-chain is mostly a repeating structure with glycine in every third position and proline or 4-hydroxyproline frequently proceeding the glycine residues. Slight differences in the primary structure establish the differences between the types of collagen. Collagen is differentiated from the accompanying extracellular matrix proteins, such as, for example, elastin and reticulin, by 1) its content of proline, hydroxyproline, and hydroxylysine, by 2) the absence of tryptophan and its low tyrosine and sulfur content, but particularly by 3) its high content of polar groups originating from the difunctional amino acids. The polar groups are responsible for the swelling properties leading eventually to dispersion of collagen in dilute acid. There is a need for compositions which alter tissue size, shape, and/or density. There is also a need for a method of altering tissue size, shape, and/or density.